MPC9448 Motorola, MPC9448 Datasheet - Page 7

• Manufacturer Part Number: MPC9448
• Description: 3.3V/2.5V LVCMOS 1:12 Clock Fanout Buffer
• Manufacturer: Motorola

cause any false clock triggering; however, designers may be
uncomfortable with unwanted reflections on the line.
better match the impedances when driving multiple lines, the
situation in Figure 6 “Optimized Dual Line Termination”
should be used. In this case, the series terminating resistors
are reduced such that when the parallel combination is added
to the output buffer impedance the line impedance is
perfectly matched.
Power Consumption of the MPC9448 and Thermal
Management
entire operating frequency range up to 350 MHz. The
MPC9448 power consumption and the associated long-term
reliability may decrease the maximum frequency limit,
depending on operating conditions such as clock frequency,
supply voltage, output loading, ambient temperture, vertical
convection and thermal conductivity of package and board.
This section describes the impact of these parameters on the
junction temperature and gives a guideline to estimate the
MPC9448 die junction temperature and the associated
device reliability. For a complete analysis of power
consumption as a function of operating conditions and
associated long term device reliability please refer to the
application note AN1545. According the AN1545, the
long-term device reliability is a function of the die junction
temperature:
P
TIMING SOLUTIONS
TOT
Since this step is well above the threshold region it will not
The MPC9448 AC specification is guaranteed for the
= V
Figure 6. Optimized Dual Line Termination
CC
MPC9448
OUTPUT
BUFFER
17Ω
⋅

17Ω + 16Ω k 16Ω = 50Ω k 50Ω
I
CCQ
f
+ V
CLOCK,MAX
P
TOT
R
R
25Ω = 25Ω
CC
S
S
=
= 16Ω
= 16Ω
⋅ f

CLOCK
=
I
CCQ
C
PD
+ V
⋅
Z
Z
Freescale Semiconductor, Inc.
⋅ N ⋅ V

O
O
T
= 50Ω
= 50Ω
N ⋅ C
1
For More Information On This Product,
CC
J
= T
⋅ f
2
CC
PD
CLOCK
A
+
⋅
+ P

Go to: www.freescale.com

T
⋅
M
TOT
J,MAX

C
N ⋅ C
R
L
⋅ R

thja
− T

To
thja
PD
+
A
+

−
7
P



M
I
junction temperature and impact the device reliability
(MTBF). According to the system-defined tolerable MTBF,
the die junction temperature of the MPC9448 needs to be
controlled and the thermal impedance of the board/package
should be optimized. The power dissipated in the MPC9448
is represented in equation 1.
MPC9448, C
output,
load, N is the number of active outputs (N is always 12 in
case of the MPC9448). The MPC9448 supports driving
transmission lines to maintain high signal integrity and tight
timing parameters. Any transmission line will hide the lumped
capacitive load at the end of the board trace, therefore,
zero for controlled transmission line systems and can be
eliminated from equation 1. Using parallel termination output
termination results in equation 2 for power dissipation.
parallel or thevenin termination, V
function of the output termination technique and DC
clock signal duty cyle. If transmission lines are used
zero in equation 2 and can be eliminated. In general, the use
of controlled transmission line techniques eliminates the
impact of the lumped capacitive loads at the end lines and
greatly reduces the power dissipation of the device. Equation
3 describes the die junction temperature T
the power consumption.
(junction to ambient) and T
According to Table 9, the junction temperature can be used to
estimate the long-term device reliability. Further, combining
equation 1 and equation 2 results in a maximum operating
frequency for the MPC9448 in a series terminated
transmission line system, equation 4.
DC
CCQ
Table 9. Die junction temperature and MTBF
C
Junction temperature (°C)
Increased power consumption will increase the die
Where I
In equation 2, P stands for the number of outputs with a
Where R
Q
L
⋅ V

⋅ I

OH
CC
⋅ V
(Μ)Σ

⋅  V

CCQ
CC
thja
100
110
120
130
PD
C
CC
L
is the thermal impedance of the package
− V
is the static current consumption of the
is the power dissipation capacitance per
represents the external capacitive output
OH
 +

1 − DC
A
is the ambient temperature.
OL
Q
, I

OL
⋅ I
MTBF (Years)
, V
OL
J
20.4
OH
⋅ V
9.1
4.2
2.0
as a function of
MPC9448
and I
OL
Equation 1

MOTOROLA
Equation 3
Equation 4
Equation 2
OH
Q
Σ
Σ
is the
are a
C
C
L
L
is
is